Mycoplasma hyopneumoniae is a respiratory pathogen associated with porcine respiratory disease complex (PRDC) and enzootic pneumonia (EP). Mycoplasma hyopneumoniae may have colonization on respiratory cilium cells to cause infection thereof to act as a cause of the swine mycoplasma pneumonia.
Mycoplasma hyopneumoniae single infection causes symptoms such as dry cough. However, when Mycoplasma hyopneumoniae is combined infection with other respiratory pathogens, this causes serious respiratory symptoms, decreases the activity of macrophages, and also causes losing a primary defense function that prevents intrusion of other pathogens, thereby to increase the risk of additional pathogen infection.
In addition to Mycoplasma hyopneumoniae, Mycoplasma hyorhinis has emerged as a new pathogen for swine respiratory infections. Mycoplasma hyorhinis has been reported to be mixed infection with swine genital respiratory virus to exacerbate the pathology. Mycoplasma hyorhinis alone is also known to cause mycoplasma (hepatic) lesions expressed in Mycoplasma hyopneumoniae. In addition, Mycoplasma hyorhinis also produce same hepatic lesions in lung as Mycoplasma hyopneumoniae dose and is a highly pathogenic pathogen.
To prevent Mycoplasma hyopneumoniae infection which causes great damage to swine farms, inactivated vaccine has currently been commercialized and used. This inactivated vaccine is currently only a vaccine available for the swine Mycoplasma pneumonia. However, most of the commercially available Mycoplasma hyopneumoniae inactivated vaccines fail to form antibodies after inoculation to the swine. Although clinical symptoms may be alleviated by the commercially available Mycoplasma hyopneumoniae inactivated vaccines, the commercially available Mycoplasma hyopneumoniae inactivated vaccines have a technical limitation in that the commercially available Mycoplasma hyopneumoniae inactivated vaccines cannot prevent natural infection and colonization of the Mycoplasma hyopneumoniae on respiratory cilium cells. Therefore, it is important to develop an effective vaccine to solve these problems.
The Mycoplasma hyopneumoniae infection is initiated when pathogens attach to the ciliates of respiratory epithelial cells. Adhesin P97 is a membrane surface protein of Mycoplasma hyopneumoniae and is known to be a highly immunogenic antigen. At a C-terminus of the P97, there are R1 and R2 sites which are repeated. The R1 site binds to an attachment site (AAKPV/E) of the host respiratory cilia. The bound Mycoplasma hyopneumoniae may obtain amino acid required for growth from the host. The Mycoplasma hyopneumoniae may cause the molecules of the host to be arranged in various ways in order to invade an injured tissue. On the other hand, the host may produce antibodies that prevent the attachment of the Mycoplasma hyopneumoniae to the swine cilium or may inhibit the growth of attached pathogens. However, previous studies have reported that conventional commercial vaccines cannot induce antibodies to P97.
Therefore, there is a need for a novel vaccine that can prevent natural infections of swine mycoplasma infection, especially Mycoplasma hyopneumoniae and Mycoplasma hyorhinis, and effectively form antibodies.